1. Field of the Invention
The invention concerns an antenna, or radiating structure, comprising an exciter patch associated with a set of radiating secondary patches.
2. Description of the Prior Art
Printed patch antennas are routinely used because their manufacturing cost is low and they are light in weight and small in size, which is particularly useful in space applications. They are generally made by etching or lithographically printing conductive patches onto dielectric substrates.
An antenna of the above kind is described in European patent application N.degree. 627 783 the title of which in translation is "Variable directive gain multilayer radiating structure". The above patent application describes an antenna in which the secondary patches are disposed in one or more planes parallel to the plane of the exciter patch.
The above antenna is very suitable for radiating in a range of directive gains from 9 dbi through 13 dbi, a range which it would be difficult to cover using individual radiators.
It has been found that antennas of the above type procure circular polarization of good quality, i.e. very low ellipticity on the axis of the antenna, perpendicular to the planes of the patches. On the other hand, the ellipticity increases significantly for directions inclined to the axis of the antenna.
The invention provides a radiating structure that maintains the purity of circular polarization over a wide angular sector.
It results from the observation that in prior art antennas the quality of polarization is degraded for inclined directions because of the nature of the coupling between the exciter patch and the radiating patches, this coupling being of the electromagnetic or proximity type.